Method for operating a gas oven and a gas oven

ABSTRACT

In the method for operating a gas oven, this has a muffle with a lower gas burner and with an upper gas burner, wherein for its control, an electronic control unit is provided for actuating two gas valves and for igniting the gas burners and also for flame monitoring. For a combination operation with upper heat and lower heat in the muffle, the upper gas burner and the lower gas burner are operated alternately to each other in each case with heating phases.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to German Application No. 10 2013 214 319.2, filed Jul. 22, 2013, the contents of which are hereby incorporated herein in its entirety by reference.

TECHNOLOGICAL FIELD

The invention relates to a method for operating a gas oven, and also to a correspondingly designed gas oven.

BACKGROUND

Electronic control units for gas ovens, which via a spark plug generate an ignition spark in order to ignite the gas burner, are known. They can also undertake flame monitoring.

BRIEF SUMMARY

The invention is based on the object of creating a method which is referred to in the introduction, and also of creating a gas oven which is suitable for its implementation, with which problems of the prior art can be avoided and with which it is possible in particular to operate a gas oven in a convenient and diverse manner using a control unit which is not excessively complicated.

This object is achieved by means of a method and also by means of a gas oven. Advantageous and also preferred embodiments of the invention are the subject of the further claims and are explained in more detail in the following text. In this case, many of the features are described only for the method or only for the gas oven. Regardless of this, however, the features shall to be able to apply independently both to the method and to the gas oven. The wording of the claims is rendered by specific reference to the content of the description.

The gas oven has a muffle as an inner chamber, in which are arranged an upper gas burner at the top and a lower gas burner at the bottom. Furthermore, a thermostat, of known design per se, is advantageously provided in the muffle for temperature regulation. The gas oven has any type of electronic control unit, for example with a DSI (Direct Spark Ignition) system in order to control the gas burners or their gas valves. With this, one associated gas valve per gas burner can be activated. Furthermore, the electronic control unit can be designed for igniting the gas burners, especially using a spark plug on the gas burner.

According to the invention, for an operating mode with top heat and bottom heat, that is to say a so-called combination operation, the upper gas burner and the lower gas burner in the muffle are operated alternately to each other, that is to say operated advantageously with heating phases in each case, and especially advantageously with pauses on each gas burner between the heating phases. This means that the upper gas burner and the lower gas burner are not in operation at the same time since this could create problems with the combustion conditions in the muffle, or ignition problems or extinguishing of the flame on the upper gas burner could occur on account of the lack of fresh air supply and air vortices on the upper gas burner due to the combustion gases of the lower gas burner. However, this combination operation with alternating operation of the upper gas burner and lower gas burner has the great advantage that heat can be supplied to the food to be cooked from the top and from the bottom. In particular, in the case of such a combi-operation an upper heating device is operated in the manner of a grill, or with the effect as a grill, since food which is to be cooked is not covered on its upper side in most cases. As a result of the alternating operation, a desired temperature for the food to be cooked can be maintained in the muffle in all cases without any problem, and can be adjusted and monitored by means of a thermostat or temperature controller. In this way, it is therefore ensured that a desired temperature prevails in the muffle for the cooking process. Furthermore, it is also possible to supply heat to the food to be cooked from the top—in the manner of an aforesaid grill—in phases and altogether over a significant time period or up to half the duration of the overall cooking process.

Such control units for gas ovens are simply known under the heading of Direct Spark Ignition. Using these control units, single-acting or double-acting solenoid valves can be actuated, wherein the gas valves are advantageously not proportional valves but designed only for opening and for closing. Consequently, one or two gas burners in one or two cavities of a gas oven can therefore be operated with such a DSI. The DSI can open and close the solenoid valves in order to supply the gas burner with gas. Furthermore, the DSI advantageously creates an ignition spark, via a spark plug, at the gas burner for igniting the gas. Also, flame monitoring can be undertaken by the control unit or by the DSI, wherein this can be advantageously carried out via an ionization current measurement. These two last-named functions can also be undertaken by a differently designed electronic control unit.

An advantageous electromechanical controller can be a thermostat. It can be mechanically adjusted to a specific predetermined temperature and then operated with a known hysteresis when this predetermined temperature is exceeded or not reached. In any case, it does not deliver permanent signals which correspond to the measured temperature but operates at a predetermined temperature or indicates that the temperature has been exceeded or not reached. When such a so-called DSI is being used, the use of such a thermostat is advantageous since it only connects the mains voltage to the corresponding input of the DSI. When a completely electronic control unit is being used, in contrast to this, the temperature in the muffle is measured by means of a thermistor, for example, and the control unit derives the heating requirement from the comparison of desired and actual temperatures. The operation according to the invention is conceivable in both embodiments, however.

In an advantageous embodiment of the invention, the upper gas burner and the lower gas burner are always operated alternately or always consecutively. This means that after a specific operating period of the upper gas burner the lower gas burner is operated and no other, and then the upper gas burner is operated again. This, on the one hand, can always be carried out consecutively in the manner of an alternating continuous power generation. Between each heating phase of one of the gas burners, that is to say either of the upper gas burner or of the lower gas burner, a pause is alternatively and advantageously made without operation of one of the gas burners. When an aforesaid thermostat or an electromechanical thermostat is being used, this pause can especially serve, for example, for slowly carrying out the heating up of the muffle, or repeatedly with short pauses between the heating phases, in order to enable a more accurate temperature measurement via the thermostat. Also, after operation of one of the gas burners, the conditions in the muffle can be normalized and disturbing vortices can also subside until the other gas burner is then ignited.

During a heating phase, a changeover from one gas burner to the other gas burner is advantageously made after a specified time. This can even be provided during the heating up of the gas oven or of the muffle. In this case, a short pause can indeed be provided without heating between two so-called partial heating phases of the gas burners, but this does not have to be so. As a result of the alternating operation of the two gas burners even during the heating up of the muffle, a uniformly distributed heating up is ensured.

In one embodiment of the invention, a thermostat for the temperature control can have a cycle time. In the event that a heating phase of one of the gas burners, especially during the heating up of the muffle, is shorter than the cycle time of the thermostat, a changeover of the gas burner during a thermostat cycle can also be carried out after a heating phase for the heating up during continuous operation of the gas burner. Therefore, the specific conditions here can be taken into account.

In an advantageous embodiment of the invention, a changeover of the operating mode of the gas oven from a purely lower-heat operation using only the lower gas burner or from a purely upper-heat operation using only the upper gas burner to a joint operation or combi-operation of both gas burners with a changeover between the two gas burners can be carried out. In this case, a currently operated gas burner can be further operated up to the end of a cycle or of the thermostat cycle before, or possibly after a short pause, a changeover to the other gas burner is made. Therefore, the operation of the gas burners, or a heating up, or an increase of the temperature in the muffle is interrupted as little as possible.

Alternatively, during a changeover of the operating mode, the previously operated gas burner can be shut down immediately, as explained before for a changeover between the gas burners. The other gas burner is then ignited either directly or, advantageously, after a certain delay time. This goes both for a preceding lower-heat operation and for a preceding upper-heat operation.

In one embodiment of the invention, it can be provided that in the event that a changeover of the operating mode of the gas oven is carried out during a pause of the gas burners, the other than the last used gas burner is operated during the next operation of the thermostat. Therefore, a changeover of the gas burners is then always carried out again, seen over a longer time.

The variation of the cycle time is advantageous only up to a certain point. If in particular a cycle time becomes excessively long, it can happen that the food to be cooked is heated for a very long time or even heated for an excessively long time from one side only and therefore unevenly. This again can be undesirable. This can especially also occur during a heating-up process.

As a result of an awkward ratio of cycle time of the temperature control and cycle time of the changeover operation, it can also happen that one burner is operated over the desired cycle time, but the other burner is stopped after several seconds by the end of the heating cycle. In this case, an inequality between the two heating modes would arise. This can be met by the interrupted cycles of the changeover operation being correspondingly continued or recovered in the respectively next heating cycle of the temperature control as compensation. Therefore, an arbitrary distribution of the changeover cycles within the thermostat cycles can ensue.

These and additional features, apart from the claims, also come from the description and the drawings, wherein the individual features can be realized by themselves in each case or in groups in the form of a sub-combination in an embodiment of the invention and in other fields and can represent advantageous and separately protectable embodiments for which protection is claimed here. The division of the application into individual sections and subheadings does not limit the statements which are made under these in their generality.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Exemplary embodiments of the inventions are represented schematically in the drawings and are explained in more detail in the following text. In the drawings:

FIG. 1 shows a schematic representation of a gas oven,

FIG. 2 shows the schematic diagram of a gas oven according to FIG. 1 with a DSI system and

FIGS. 3 to 11 show different possible changeover operations of gas burners in the gas oven.

DETAILED DESCRIPTION

Shown schematically in FIG. 1 is an oven 11 with a muffle 12 in which are arranged an upper gas burner 14 and a lower gas burner 16. The gas burners 14 and 16 are designed as are basically known in the prior art. The upper gas burner 14 is supplied via a gas valve 18 and the lower gas burner 16 is supplied via a gas valve 20, wherein the two gas valves can be integrated physically or constructionally in a sub-assembly. Also, two gas valves can be connected in series in a burner train in order to fulfill the requirements for operational safety in the case of malfunction of one gas valve. The gas valves 18 and 20 are connected to a control unit 22 of the gas oven 11 which can operate electromechanically or electronically and is correspondingly designed or consists of one or more components. Furthermore, provision is additionally made in the muffle 12 for a temperature sensor which is advantageously designed as an electromechanical thermostat 24 or thermistor. It is connected to the control unit 22 and delivers a signal to this in a known manner.

Shown in FIG. 2 is a schematic diagram for a gas oven 11 with a DSI system as the control unit. Spark plugs 26 and 28 for the ignition are shown here on the gas burners 14 and 16. The spark plugs 26 and 28 are connected to a DSI 34. Thermoelements are not provided here since flame monitoring is carried out by means of known ionization current measurement. Furthermore, the gas oven 11 or its control unit 22 additionally has a switch for selecting the baking mode, a thermostat 24 for temperature control via its temperature sensor, a timer 36, a door switch 38, an oven lamp 40 and an operating indicator 42.

In the case of an under-heat operating mode, the output of the thermostat 24 is connected via the corresponding contact bank of the selector switch to a so-called heat-request channel of the DSI 34 which is associated with the lower gas burner 16. If mains voltage is applied to the heat-request channel then the gas valve of the corresponding burner is opened and ignition initiated. In the upper-heat operating mode, the output of the thermostat is connected to the heat-request channel of the DSI 34 which is associated with the upper gas burner 14. In the combined operating mode with upper heat and lower heat, the output of the thermostat 24 is connected to both heat-request channels of the DSI 34. An alternating operation between the gas burners 14 and 16 is then carried out, that is to say when both heat-request channels are energized or engaged at the same time or delayed by only fractions of a second. In this case, according to the invention only one of the two gas burners is ignited since both are certainly never to be operated together. The selection of the gas burner can be carried out arbitrarily or according to predetermined programming. This can be seen with reference to FIG. 3, for example.

In FIG. 3, the temperature in the muffle 12 is plotted on the vertical axis, specifically at a focal point. Shown in the line “active burner” is which of the two gas burners 14 or 16 is operated or is active. The center line stands for upper-heat heat request and the lowest line stands for lower-heat heat request. Both indicate the input for the respective gas burner 14 or 16 on the DSI 34.

According to FIG. 3, only the upper gas burner 14 for upper heat OH is operated first of all. For this, it is ignited by the spark plug 26 and supplied with gas by means of the gas valve 18. Since the gas valves 18 and 20 are advantageously not generally proportional valves but only fully open or fully close, the gas burners can only operate with a fixed, predetermined momentary output, specifically their full load or rated load. In the alternative procedure according to FIG. 4, it is to be seen how at the start it begins with the lower gas burner 16 as lower heat UH, which is ignited by the spark plug 28 and supplied with gas by means of the gas valve 20. Which of the two gas burners 14 or 16 is used first can either be purposefully stored in software in the control unit 22 or, alternatively, it can be selected randomly.

From the views of FIGS. 3 and 4, it is to be seen that for a time only the first started gas burner is active first of all. Then, it is shut down for a pause, especially if the temperature has achieved a value—detected by the thermostat 24 and predetermined by an operating element—corresponding to the wish of an operator. Then, a phase or pause or break without heating is carried out, as is generally known in the case of two-step controllers. After this, an operating phase with heating up of the muffle 12 is carried out again, but naturally with the other gas burner.

From the two lower lines along the X-axis, it is to be seen that during the operating phases a heat request exists in each case for both gas burners 14 and 16. The control unit 22 or the DSI 34 then engages the gas burners but in an alternating manner.

Furthermore, it is known that a clock time or cycle time t_(T,in) or t_(T,out) of the thermostat depends on its hysteresis, a position of the thermostat sensor in the muffle 12, the thermal insulation of the oven 11 or of the muffle 12, the heat output and the predetermined temperature. Therefore, a cycle time of the thermostat can vary, as is to be seen from FIG. 5 with a relatively long cycle time. In comparison to this, in FIGS. 3 and 4 short cycle times exist and therefore also less fluctuating of the temperature. In the case of such long cycle times, there is the risk, however, that food to be cooked is heated for a relatively long time on one side only and therefore unevenly. This should be avoided. This, however, is the case not only in the case of relatively long cycle times according to FIG. 5 but naturally also during the heating up, especially if according to FIGS. 3 and 5 the heating up is started using the upper gas burner 14, or upper heat, since the risk of burning is especially great in this case.

In order to avoid such an excessively long, uneven heat input, in a further embodiment of the invention it can simply be provided that the gas burners are changed over after a firmly established or predetermined time. This is shown in FIG. 6 for a thermostat with a relatively long cycle time. In this case, a start is made—either in a controlled or arbitrary manner—with one of the gas burners 14 or 16, this being just with the lower gas burner 16 as lower heat UH in FIG. 6. This is operated for a time t_(UH,in) which is stored in the program run of the control unit 22. This can be 30 seconds to 120 seconds, for example. After this, the lower gas burner 16 is extinguished and a short delay time t_(UH,out) follows as a pause. During this time, the atmosphere in the muffle 12 is normalized so that the upper gas burner 14 can ignite and be operated without any problem, specifically for a time t_(OH,in). Again, a pause as a delay time t_(OH,out) follows this. These four times are selected according to the conditions in the gas oven 11 or in the muffle 12 and according to a desired ratio between upper heat OH and lower heat UH. In the case the time t_(UH,in) is shorter than the cycle time t_(T,in) of the thermostat, as is shown in FIG. 6, a changeover of the gas burners is carried out not only during the heating up but also in the steady state. This is simply to be seen in FIG. 6 with a changeover from the lower gas burner 16 to the upper gas burner 14 during the cycle time t_(T,in). This is therefore a relatively longer thermostat cycle than previously described. If, however, the time t_(UH,in) or the time t_(OH,in) is greater than the cycle time t_(T,in), then no changeover is carried out within a thermostat cycle but only at the next cycle. This is to be seen in FIG. 7, in which after the heating-up phase only one of the two burners 14 or 16 is operated in each case during a relatively short thermostat cycle t_(T,in).

Alternatively, it is also possible, however, that a changeover cycle of a gas burner, which has been interrupted by the cycle of the thermostat before its end, is recovered in the next cycle. Therefore, an arbitrary distribution of the changeover cycles within the thermostat cycles ensues—see FIG. 11.

Shown in FIG. 8 is how a changeover of the operating mode of the gas oven 11 is carried out. At the beginning, a lower heat operation using only the lower gas burner 16 exists. If, during a cycle time t_(T,in), a changeover is made from the lower-heat operating mode to a combination operation at a time point which is vertically drawn in by a dashed line, then in a first alternative the currently operated burner can be further operated up to the end of the cycle. In FIG. 8, it is to be seen in particular that during the second engagement of the lower gas burner 16 a heat request for upper heat OH already exists. Alternatively, it is also possible that the previously operated gas burner—in this case the lower gas burner 16—is immediately shut down. The other gas burner—in this case the upper gas burner 14—can then be ignited after a delay time or pause for stabilizing the conditions in the muffle 12. This is to be seen in FIG. 9.

If a changeover between the gas burners 14 and 16 is carried out during the time t_(T,out), then with the next operation of the thermostat not the last used, but the other, gas burner is operated. This is to be clearly seen in FIG. 10 at the time point of the vertical dashed line. After this, a heat request for the upper heat OH then exists and the upper gas burner 14 is directly operated or fired as the active burner.

In a once more further development stage of the invention, it is also conceivable that during the program run, t_(T,in) and t_(T,out) are measured and from this the optimum values for the other four described times are calculated. Furthermore, in the best case the times t_(OH,out) and t_(UH,in) are even close to zero so as not to interrupt a heat supply for an unnecessarily long time.

If instead of the electromechanical thermostat together along with a thermostat sensor 24 an electronic control unit is used, that is to say without DSI, with a temperature-dependent resistance as a temperature sensor, it is possible to continuously access measured values of the temperature sensor. As in the case of a DSI, there is no dependency upon “in” or “out” signals which the thermomechanical thermostat delivers. 

That which is claimed:
 1. A method for operating a gas oven, wherein said gas oven has a muffle with a lower gas burner and with an upper gas burner and with gas valves for said burners, wherein for controlling said gas burners, an electronic control unit is provided for actuating said gas valves and for igniting said gas burners and also for flame monitoring, wherein for an operating mode with upper heat and lower heat in said muffle said upper gas burner and said lower gas burner are operated alternately to each other.
 2. The method as claimed in claim 1, wherein temperature controlling in the gas oven is carried out via an electromechanical thermostat or via a temperature controller.
 3. The method as claimed in claim 1, wherein said upper gas burner and said lower gas burner are always operated alternately and always operated consecutively.
 4. The method as claimed in claim 3, wherein said upper gas burner and said lower gas burner are never operated at the same time.
 5. The method as claimed in claim 1, wherein between each heating phase either of said upper gas burner or of said lower gas burner a pause is provided without operation of a gas burner.
 6. The method as claimed in claim 1, wherein during a heating phase, a changeover is made from one said gas burner to the other said gas burner after a specified time.
 7. The method as claimed in claim 6, wherein said changeover is made during the heating up of said gas oven or of said muffle with a short pause without heating between two heating phases of said gas burners.
 8. The method as claimed in claim 1, wherein a thermostat for temperature control has a cycle time as a thermostat cycle, wherein in the event that a heating phase of one of said gas burners is shorter than said cycle time of said thermostat, also after a heating phase for said heating up during continuous operation of said gas burner, a changeover of said gas burner is carried out during said thermostat cycle.
 9. The method as claimed in claim 8, wherein said event is during said heating up of said muffle.
 10. The method as claimed in claim 1, wherein a thermostat for temperature control has a cycle time as a thermostat cycle, wherein in the event that a heating phase of one of said gas burners is carried out during said changeover of said gas burner during said thermostat cycle, a residual time of one of said gas burners, which residual time remains after an interruption of said thermostat cycle, is recovered in a next thermostat cycle.
 11. The method as claimed in claim 1, wherein during a changeover of said operating mode of said gas oven from a lower-heat operation of only said lower gas burner or from an upper-heat operation of only said upper gas burner to a joint operation of both said gas burners with changeover between said gas burners, a currently operated gas burner is further operated up to an end of a cycle or of a thermostat cycle.
 12. The method as claimed in claim 1, wherein during a changeover of said operating mode of said gas oven from a lower-heat operation of only said lower gas burner or from an upper-heat operation of only said upper gas burner to a joint operation of both said gas burners with changeover between said gas burners, said previously operated gas burner is immediately shut down and after a certain delay time said other gas burner is ignited.
 13. The method as claimed in claim 1, wherein in an event that a changeover of said operating mode of said gas oven is carried out during a pause of said gas burners, the other gas burner than said last used gas burner is operated during next operation of said thermostat.
 14. A gas oven for implementing said method as claimed in claim 1, comprising: said gas oven having a muffle in which are arranged an upper gas burner at the top of said muffle and a lower gas burner at the bottom of said muffle, and wherein in said muffle also a temperature sensor is provided for temperature control in said muffle, wherein said gas oven is provided with an electronic control unit.
 15. A gas oven for implementing said method as claimed in claim 1, comprising: said gas oven having a muffle in which are arranged an upper gas burner at the top of said muffle and a lower gas burner at the bottom of said muffle, and wherein in said muffle also a temperature sensor is provided for temperature control in said muffle, wherein said gas oven is provided with a control unit, which after connection of a corresponding input to a mains potential activates firing of said corresponding gas burner. 